Thermal processing is commonly practiced in the semiconductor industry. Semiconductor substrates are subjected to thermal processing in the context of many transformations, including deposition, doping, activation, and annealing of gate source, drain, and channel structures, siliciding, crystallization, oxidation, and the like. Over the years, techniques of thermal processing have progressed from simple furnace baking, to various forms of increasingly rapid thermal processing (RTP), spike annealing, as well as other thermal processes.
As the critical dimensions of semiconductor device features continue to shrink, more stringent constraints on thermal budgets are required during thermal processes. Many of the aforementioned thermal processes utilize lamp heating in the form of a lamphead consisting of a plurality of light sources positioned to direct radiant energy toward a substrate. However, the high intensity lamps utilized in the lamphead create high temperatures within the material of the lamphead. This temperature must be controlled for many processes to enable cooling of the substrate. For example, during RTP, thermal radiation from the lamps is generally used to rapidly heat a substrate in a controlled environment to a maximum temperature of up to about 1,350 degrees Celsius. This maximum temperature is maintained for a specific amount of time ranging from less than one second to several minutes depending on the process. The substrate is then cooled to room temperature for further processing. To enable the cooling to room temperature, the lamphead must be cooled. However, control of the temperature of the lamphead is difficult based on many factors. Additionally, the irradiance pattern of the light sources is sometimes irregular in conventional lampheads, which creates irregular heating of the substrate.
What is needed is a method and apparatus that enables improved temperature control of the lamphead within a thermal process chamber.